Computerized Tomography or CT modality has been widely used for diagnosis purposes. It can provide very detailed anatomical structures of human organs. In oncology, CT is used to monitor therapeutic responses of a treatment to tumors by measuring size changes. However, it may take a long time, e.g., several months, for a treatment to be reflected in the size change of a tumor. Contrastingly, Single Photon Emission Computed Tomography (“SPECT”) is a modality that can provide immediate metabolic measurement of a human organ and/or tumors, allowing one to discriminate healthy tissue from diseased tissue at the functional level. However, while both SPECT and CT devices provides imaging, the imaging from the SPECT device cannot provide the detailed anatomical structural information about the human organs the way CT does. Recently, however, CT and SPECT have been combined into one imaging device, allowing both CT and SPECT images to be taken in one image session.
Currently, the utilization of SPECT-CT imaging stays mostly at the image level. For example, in liver functional measurement in SPECT, physicians usually manually trace the left and right lobe boundaries of the liver in SPECT and compute the isotope counts to measure the lobe's liver functions. However, in percutaneous treatment planning for liver lesions, such as by Radio-Frequency Ablation (RFA) or chemoembolization, it is desirable to measure liver functions in local regions or interested lobe segments. For example, it is desirable to measure the liver function of a blood supply or blood drainage territory of a vascular structure. Since SPECT does not provide information about detailed anatomical structures, operating with the SPECT images alone cannot perform the above task. Although SPECT and CT image devices may provide mechanical registration between the SPECT image space and CT image space, the transformation may only be used for a rough alignment of the SPECT and CT images. Since SPECT and CT images are acquired in different time, breathing and body motion can cause non-rigid deviation from the mechanical registration. Thus, analysis in the CT space cannot be readily applied to the SPECT space.
It is therefore highly desirable to be able to accurately measure the liver functions of a local region or liver segments in SPECT by using anatomical information in CT. It is also desirable to perform such measurement in real-time and in an interactive manner.